Why take him to such a difficult spot to access? There's many easier spots that would be more appropriate. If you were so prepared why didn't you use your compass or GPS? Do you leave the tape after you hike out or do you take it out with you? Maybe the guy who removed it has seen tape left all over the place and has gotten sick of it. If you're such and experienced bushman you know there are many ways to mark a trail such as breaking branches as u hike, making marks on the ground with your feet, using sticks as way points and so on which are less intrusive. Heck I have used pine cones and little pieces of branches placed with the cone so I know I placeD it and it's not one that fell off a tree. I have seen some people who actually make HUGE arrows out of branches to make trail heads..... If you can't find the trail heads without a massive billboard sign you may as well stick to the C-V system. The chehalis is unique in the fact that it's more prestine and natural, it's not a meat market like the C-V system. The regulars like it that way and want to keep it that way.
I hunt extensively as well as fish. As a result I have probably had to mark several trails, most to be hiked out in the dark because I hunt til last light. All of the examples you listed (breaking branches, marking the ground, using pine cones, and huge arrows) are either of very little help, or dangerous. Breaking branches can be dangerous depending on height, ground marks are easily destroyed or covered by leaf litter or rain, trying to find something the size of a pine cone is in the dark is very difficult and time is often wasted looking for the next one unless it is close to the previous. As for the large branches to mark trail heads, what happens when you are 1/3 yards up the trail and not sure where to go? A trail only has 2 heads, very very few get injured there. Accidents happen along the body, the where the trail markers are placed.
Should the poster have taken his friend down that trail? I have no idea, too many unanswered questions. Is his back always going out, or it an known risk that only happens occasionally. Is he able to hike for say 30 minutes, but it took significantly longer than that because someone removed the tape. Did stress play a role. Did he slip because he went off the trail because someone removed the trail markers. Glad people like you are able know the answer to all of these questions with the information provided.
I agree that the reason the Chehalis is so nice is that it isn't the C/V. If you want to fish it you have to work for it. But do not tell me it is pristine. There are generations of people who have been fishing that river; every trail you walk, every hole you fish has been fished by someone before you. And it will be fished be someone long after you or I am gone. Let them enjoy it and be safe.
P.S.: For those that care, they do make biodegradable trail marker tape. But in all honesty T.P. designed for use in a trailer is much more effective. It stands out, breaks down rapidly in a few rains, and you should carry it with you anyway.